U.S. patent number 8,084,083 [Application Number 13/008,537] was granted by the patent office on 2011-12-27 for method for manufacturing an anisotropic conductive adhesive sheet.
This patent grant is currently assigned to Asahi Kasei EMD Corporation. Invention is credited to Koya Matsuura, Akira Otani.
United States Patent |
8,084,083 |
Otani , et al. |
December 27, 2011 |
Method for manufacturing an anisotropic conductive adhesive
sheet
Abstract
A method for manufacturing an anisotropic conductive adhesive
sheet is disclosed. The sheet comprises at least a curing agent, a
curable insulating resin, and conductive particles. The method
comprises providing an adhesive layer on a biaxially stretchable
film to form a laminate, densely packing conductive particles
having an average particle size of 1 to 8 .mu.m on the laminate to
form a conductive particle-attached film, biaxially stretching and
holding the conductive particle-attached film so that the average
particle distance between adjacent conductive particles is at least
one to five times or less the average particle size of the
conductive particles and not greater than 20 .mu.m. The conductive
particles are transferred to an adhesive sheet containing at least
a curing agent and a curable insulating resin and having a
thickness of at least 1.5 times the average particle distance
between the conductive particles but not greater than 40 .mu.m.
Inventors: |
Otani; Akira (Fuji,
JP), Matsuura; Koya (Fuji, JP) |
Assignee: |
Asahi Kasei EMD Corporation
(Tokyo, JP)
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Family
ID: |
34650245 |
Appl.
No.: |
13/008,537 |
Filed: |
January 18, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110114256 A1 |
May 19, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10595914 |
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PCT/JP2004/017944 |
Dec 2, 2004 |
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Foreign Application Priority Data
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Dec 4, 2003 [JP] |
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2003-406108 |
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Current U.S.
Class: |
427/174;
427/205 |
Current CPC
Class: |
H05K
3/323 (20130101); H01R 4/04 (20130101); H05K
2203/0271 (20130101); H05K 2203/0191 (20130101); Y10T
428/25 (20150115); Y10T 428/256 (20150115); H05K
2201/10378 (20130101); Y10T 428/254 (20150115) |
Current International
Class: |
B05D
1/12 (20060101) |
Field of
Search: |
;427/174,205 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1128040 |
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Jul 1996 |
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CN |
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1307625 |
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Aug 2001 |
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CN |
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2-117980 |
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May 1990 |
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JP |
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6-045024 |
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Feb 1994 |
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JP |
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6-060712 |
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Mar 1994 |
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JP |
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6-349339 |
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Dec 1994 |
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JP |
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2895872 |
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Mar 1999 |
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JP |
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11-121072 |
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Apr 1999 |
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JP |
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2000-149677 |
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May 2000 |
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JP |
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2000-178511 |
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Jun 2000 |
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JP |
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3165477 |
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Mar 2001 |
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JP |
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2002-519473 |
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Jul 2002 |
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JP |
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2002-358825 |
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Dec 2002 |
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JP |
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2003-064324 |
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Mar 2003 |
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JP |
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Other References
International Search Report for PCT/JP2004/017944, mailed Feb. 15,
2005. cited by other .
Chinese Office Action issued with respect to patent family member
Chinese Application No. 200910117908.X, issued Dec. 16, 2010, along
with an English-language translation. cited by other .
Japanese Office Action issued with respect to Japanese Patent
Application No. 2005-515962, issued Mar. 23, 2011. cited by
other.
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Primary Examiner: Parker; Frederick
Attorney, Agent or Firm: Greenblum & Bernstein, PLC
Parent Case Text
RELATED APPLICATIONS
This application is a divisional of U.S. application Ser. No.
10/595,914 filed May 19,2006, now abandoned, which is a national
stage international application of PCT/JP2004/017944, filed Dec. 2,
2004, which claims priority to Japanese application No.
2003-406108, filed Dec. 4, 2003. The disclosure of application No.
10/595,914 and PCT/JP2004/017944 are incorporated by reference
herein in their entireties.
Claims
What is claimed is:
1. A method for manufacturing an anisotropic conductive adhesive
sheet comprising at least a curing agent, a curable insulating
resin, and conductive particles, said method comprising providing
an adhesive layer on a biaxially stretchable film to form a
laminate, densely packing conductive particles having an average
particle size of 1 to 8 .mu.m on the laminate to form a conductive
particle-attached film, biaxially stretching and holding the
conductive particle-attached film so that the average particle
distance between adjacent conductive particles is one to five times
the average particle size of the conductive particles and not
greater than 20 .mu.m, and transferring the conductive particles to
an adhesive sheet containing at least a curing agent and a curable
insulating resin and having a thickness of at least 1.5 times the
average particle distance between the conductive particles but not
greater than 40 .mu.m.
Description
TECHNICAL FIELD
The present invention relates to an anisotropic conductive adhesive
sheet that has excellent microcircuit connecting properties, and a
connecting structure.
BACKGROUND ART
Heretofore, concerning an anisotropic conductive adhesive sheet for
connecting microcircuits, various conductive particles and
anisotropic conductive adhesive compositions have been examined in
order to improve connecting properties and prevent
short-circuiting. For example, heretofore known methods include a
method wherein insulating particles having a coefficient of thermal
expansion equivalent are compounded to conductive particles (see
Patent Document 1); a method wherein insulating particles are
deposited on the surfaces of conductive particles in order to
prevent short-circuiting (see Patent Document 2); a method wherein
the surfaces of conductive particles are coated with an
electrically insulating resin (see Patent Document 3); a method
wherein layers containing and not containing conductive particles
are stacked to prevent short-circuiting between adjacent circuits
(see Patent Document 4); a method wherein a terminal circuit is
coated with a photosensitive resin, parts other than a connecting
part are selectively cured to make such parts not adhesive, and
conductive particles are deposited on the part having adhesion and
then coated with an adhesive resin to prevent short-circuiting
between adjacent circuits (see Patent Document 5); a method wherein
a peeling liner having a depression is previously formed, a single
or plurality of conductive particle is disposed in the depression,
and it is deposited on an adhesive layer to fabricate an
anisotropic conductive adhesive sheet (see Patent Document 6); and
a method wherein a biaxially stretchable sheet is coated with
conductive particles, the coated sheet is stretched within a range
not exceeding the particle diameter of the conductive particles,
and the isolated conductive particles are transferred into the
adhesive layer to fabricate an anisotropic conductive adhesive
sheet (see Patent Document 7).
However, in the conventional art wherein insulating properties are
imparted to conductive particles or the like, there was limitation
to micronize the particle diameter of conductive particles for
insulating coating or insulating coating deposition, and both the
security of insulating properties and the security of number of
connecting particles could not be satisfied in the case of
microcircuit connecting. Also in the conventional art for
preventing short-circuiting by adhesive compositions, the security
of insulation properties and electrical connecting properties were
not simultaneously satisfied in the case of microcircuit
connecting. Furthermore, in Patent Document 6, although an example
wherein a peeling liner having a depression is previously formed
and a single or plurality of conductive particle is disposed in the
depression is disclosed, no examples wherein this is deposited on
the adhesive layer to form an anisotropic conductive adhesive sheet
are disclosed. It was actually difficult to dispose a single
conductive particle in each depression shallower than the particle
diameter of the conductive particle. To the contrary, although a
single conductive particle could be disposed in each depression
deeper than the particle diameter of the conductive particle, it
was difficult to deposit on the adhesive layer. As a result, the
obtained anisotropic conductive adhesive could not satisfy both the
security of insulating properties and the security of number of
connecting particles. Also since the anisotropic conductive
adhesive sheet disclosed in Patent Document 7 is based on a
technical idea to secure electrical conductivity by sandwiching
conductive particles between terminals themselves and at the same
time to secure insulating properties by fixing conductive
particles, the particle diameter of conductive particles distance
between adjacent conductive particles and the film thickness of the
anisotropic conductive adhesive sheet must be of substantially the
same values. Therefore, the gaps in the lateral direction of a
terminal to be coupled were not filled with the insulating resin,
and insulation properties were not be satisfied. Connecting
properties of terminals themselves were also not satisfactory due
to a small amount of resin. In view of the security of electrical
conductivity, the distance between adjacent conductive particles
cannot exceed the particle diameter of the conductive particles,
and particularly in the case of microcircuit connecting, it is
difficult to satisfy both the security of insulating properties and
the security of electrical connecting properties at the same
time.
Patent Document 1: JP-A-6-349339
Patent Document 2: JP Patent No. 2895872
Patent Document 3: JP Patent No. 2062735
Patent Document 4: JP-A-6-45024
Patent Document 5: JP Patent No. 3165477
Patent Document 6: JP-A-2002-519473
Patent Document 7: JP-A-2-117980
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
It is an object of the present invention to provide an anisotropic
conductive adhesive sheet that realizes favorable electrical
connecting properties without impairing insulation properties
between adjacent circuits of a microcircuit, a method for the
manufacture thereof and a connecting structure using the same.
Means for Solving the Problems
As a result of extensive studies to solve the above-described
problems, the present inventors have found that the problems can be
solved by the use of an anisotropic conductive adhesive sheet
characterized in that conductive particles having a certain average
particle size are present in a certain range without contact with
at least a certain proportion of conductive particles.
Specifically, the present invention provides the followings. (1) An
anisotropic conductive adhesive sheet comprising at least a curing
agent, a curable insulating resin and conductive particles, wherein
90% or more of the conductive particles are present in a region of
a thickness of not greater than 2.0 times the average particle size
of the conductive particles extending from one surface of the
anisotropic conductive adhesive sheet in the thickness direction,
and 90% or more of the conductive particles are present without
contact with other conductive particles, wherein the average
particle size of the conductive particles is 1 to 8 .mu.m, and the
average particle distance between adjacent conductive particles is
at least once but five times or less the average particle size and
not greater than 20 .mu.m, and wherein the thickness of the
anisotropic conductive adhesive sheet is at least 1.5 times the
average particle distance but not greater than 40 .mu.m. (2) The
anisotropic conductive adhesive sheet according to (1), wherein the
conductive particles are at least those selected from the group
consisting of noble metal-coated resin particles, noble
metal-coated metal particles, metal particles, noble metal-coated
alloy particles, and alloy particles. (3) A method for
manufacturing an anisotropic conductive adhesive sheet comprising
providing an adhesive layer on a biaxially stretchable film to form
a laminate, densely packing conductive particles having an average
particle size of 1 to 8 .mu.m on the laminate to form a conductive
particle-attached film, biaxially stretching and holding the
conductive particle-attached film so that the average particle
distance between adjacent conductive particles is at least once (1)
but five (5) times or less the average particle size of the
conductive particles and not greater than 20 .mu.m, and
transferring the conductive particles to an adhesive sheet
containing at least a curing agent and a curable insulating resin
and having a thickness of at least 1.5 times the average particle
distance between the conductive particles but not greater than 40
.mu.m. (4) The method according to (3), wherein the biaxially
stretchable film is a long film and the adhesive sheet is a long
adhesive sheet. (5) A method for electrically connecting an
electronic circuit component having fine connecting terminals to a
circuit board having a circuit corresponding thereto using an
anisotropic conductive adhesive sheet, comprising electrically
connecting the electronic circuit component to the circuit board
having a circuit corresponding thereto using the anisotropic
conductive adhesive sheet according to (1) or (2), wherein said
electronic circuit component has a height of the fine connecting
terminals of 3 to 15 times the average particle distance between
conductive particles and not greater than 40 .mu.m, a distance
between the fine connecting terminals of 1 to 10 times the average
particle distance and not greater than 40 .mu.m, and a pitch of the
fine connecting terminals of 3 to 30 times the average particle
distance and not greater than 80 .mu.m. (6) A fine connecting
structure obtained by the method according to (5).
Advantages of the Invention
The anisotropic conductive adhesive and connecting structure of the
present invention have favorable insulating characteristics between
adjacent circuits, and have favorable electrical connecting
properties between coupled circuits. The present invention also
exerts the above-described effect particularly in the connecting of
microcircuits.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be specifically described below.
First, conductive particles in the present invention will be
described. In the present invention, although heretofore known
conductive particles can be used, it is preferable to use at least
those selected from the group consisting of noble metal-coated
resin particles, noble metal-coated metal particles, metal
particles, noble metal-coated alloy particles, and alloy particles.
More preferably, these particles have melting points not higher
than 500.degree. C. As the noble metal-coated resin particles, the
use of spherical particles of polystyrene, benzoguanamine,
polymethyl methacrylate or the like coated with nickel and gold in
this order is preferable. As the noble metal-coated metal
particles, the use of particles of a metal, such as nickel and
copper, coated with a noble metal, such as gold, palladium and
rhodium, on the outermost layer is preferable; and as the noble
metal-coated alloy particles, the use of alloy particles described
below coated with a noble metal, such as gold, palladium and
rhodium, on the outermost layer is preferable. As coating methods,
thin-film forming methods such as vapor deposition and sputtering,
coating methods by dry blending, or wet processes such as
electroless plating and electrolytic plating, can be used. In view
of mass productivity, an electroless plating method is preferable.
As metal particles and alloy particles, the use of one or two or
more selected from the group consisting of metals, such as silver,
copper and nickel is preferable. As alloy particles, the use of
low-melting-point alloy particles having a melting point of
500.degree. C. or below is preferable, and furthermore, the use of
low-melting-point alloy particles having a melting point of
350.degree. C. or below is more preferable because metallic bond
can be formed between connecting terminals and from the viewpoint
of connecting reliability. When low-melting-point alloy particles
are used, it is preferable to previously coat the particle surfaces
with flux or the like. Coating with so-called flux is preferable
because oxides or the like on the surface can be removed. As the
flux, a fatty acid or the like, such as abietic acid, can be
used.
The ratio of the average particle size to the maximum particle
diameter of the conductive particles is preferably 2 or less and
more preferably 1.5 or less. It is preferable that the particle
size distribution of the conductive particles is narrower, and the
geometric standard deviation of the particle size distribution of
the conductive particles is preferably 1.2 to 2.5 and more
preferably 1.2 to 1.4. If the geometric standard deviation is
within the above-described values, the variation of the particle
diameters is reduced. Normally, when a constant gap is present
between two terminals to be connected, it is considered that the
more even the particle diameters, the more effectively conductive
particles function.
The geometric standard deviation of particle size distribution
means the value obtained by dividing the a value of the particle
size distribution (the particle diameter value at 84.13%
accumulation) by the particle diameter value at 50% accumulation.
When particle diameters (logarithm) are set on the abscissa of the
particle size distribution graph and the cumulative values
(percent, cumulative number ratio, logarithm) are set on the
ordinate, the particle size distribution becomes substantially
straight line, and the particle size distribution follows
logarithmic normal distribution. The cumulative value means the
ratio of the number of particles having a certain particle diameter
and smaller to the total number of particles expressed in
percentage. The sharpness of particle size distribution is
expressed by the ratio of .sigma. (the particle diameter value at
84.13% accumulation) to the average particle size (the particle
diameter value at 50% accumulation). The .sigma. value is a reading
value from an actual measured value or a plotted value in the above
graph. The average particle size and particle size distribution can
be measured using heretofore known methods and instruments, and for
the measurements, a wet particle size distribution meter, laser
particle size distribution meter, or the like can be used.
Alternatively, the particles can be observed using an electron
microscope or the like and the average particle size and particle
size distribution can be calculated. The average particle size and
particle size distribution in the present invention can be obtained
using a laser particle size distribution meter.
The average particle size of the conductive particles is 1 to 8
.mu.m, preferably 2 to 6 .mu.m. In view of insulation properties, 8
.mu.m or less is preferable, and the effect of variation in the
height of connecting terminals or the like is insignificant; and in
view of electrical connecting, 1 .mu.m of more is preferable.
The average particle distance to adjacent conductive particles is
not greater than 20 .mu.m and at least once to five times,
preferably at least 1.5 to 3 times the average particle size. In
view of preventing particle coagulation due to particle flow in
connecting and securing insulation properties, not less than once
the average particle size is preferable; and in view of fine
connecting, not greater than five times is preferable.
In the present invention, adjacent conductive particles mean 6
particles closest to an optionally selected conductive particle.
The method for measuring the average particle distance to the
adjacent conductive particles is as follows.
A photo enlarged by an optical microscope is taken, optional 20
particles are selected, distances to 6 particles closest to each
particle are measured, and the average value of the total is
obtained to make it the average particle distance.
The thickness of the anisotropic conductive adhesive sheet is at
least 1.5 times the average particle distance but not greater than
40 .mu.m and preferably at least twice the average particle
distance but not greater than 40 .mu.m. In view of mechanical
connecting strength, not less than 1.5 times is preferable; and in
view of preventing decrease in the number of coupled particles due
to particle flow in connecting, not greater than 40 .mu.m is
preferable. The compounding quantity of conductive particles is
preferably 0.5 parts by mass to 20 parts by mass relative to 100
parts by mass, more preferably 1 part by mass to 10 parts by mass
of the components containing a curing agent and a curable
insulating resin. In view of insulating properties, not greater
than 20 parts by mass is preferable; and in view of electrical
connecting properties, not less than 0.5 parts by mass is
preferable.
Next, the anisotropic conductive adhesive sheet of the present
invention will be described. In the anisotropic conductive adhesive
sheet of the present invention, 90% or more of the conductive
particles are present in a region of a thickness of not greater
than 2.0 times the average particle size of the conductive
particles extending from one surface of the anisotropic conductive
adhesive sheet in the thickness direction; however, it is
preferable that 90% or more of them are present in a region of 1.5
times, it is more preferable that 95% or more of them are present
in a region of 2.0 times, and it is further preferable that 95% or
more of them are present in a region of 1.5 times. Specifically,
when the average particle size is 3.0 .mu.m, "in a region of 2.0
times" means in a region of a thickness of 6.0 .mu.m in the
anisotropic conductive composition, and "90% or more of them are
present in the region" means that 90% or more of the conductive
particles are present in the layer of the thickness of 6.0 .mu.m.
In the anisotropic conductive adhesive sheet of the present
invention, as the position where the conductive particles are
present to the thickness direction of the anisotropic conductive
adhesive sheet, the values of the positions of randomly selected
100 conductive particles measured using a laser microscope or the
like that can measure the displacement of the focal direction are
used. At the same time, the number of conductive particles present
without contact with other conductive particles can also be
measured. When the displacement of the focal direction is measured
using the laser microscope, the resolution of displacement
measurement is preferably 0.1 .mu.m or less, and more preferably
0.01 .mu.m or less. As the average particle size of the conductive
particles, the value previously measured separately using a laser
particle size distribution meter or the like is used. The thickness
of the anisotropic conductive adhesive sheet of the present
invention is preferably 3 to 20 times, more preferably 5 to 10
times the average particle size of the conductive particles. From
the aspect of adhesion strength of the connecting structure, not
less than 3 times is preferable; and from the aspect of connecting
properties, less than 20 times is preferable. From the aspect of
connecting properties, the region of not more than 2.0 times the
average particle size of the conductive particles where 90% or more
conductive particles are present is preferably outside the center
portion in the thickness direction of the conductive adhesive
sheet, and more preferably, a part of the conductive particles are
exposed on the surface of the anisotropic conductive adhesive
sheet. The region of not greater than 2.0 times the average
particle size of the conductive particles is preferably within 1/2,
more preferably 1/3 the thickness of the sheet in the thickness
direction form the surface of the conductive sheet. It is also
preferable that a part of the conductive particles are exposed on
the surface of the anisotropic conductive adhesive sheet.
Next, a method for manufacturing an anisotropic conductive adhesive
sheet characterized in that conductive particles in the present
invention are present without contact with other conductive
particles will be described. In the present invention, "conductive
particles are present without contact with other conductive
particles" means that each of the conductive particles is present
alone without coagulation. Hereafter, the expression "present
alone" or "single particle" may be used for this meaning. Although
known methods can be used as the method for manufacturing the
anisotropic conductive adhesive sheet of the present invention, a
method is preferable wherein a single layer of conductive particles
are arranged on a stretchable film or sheet, the conductive
particles are dispersed and arrayed by stretching it, and they are
transferred onto an adhesive sheet composed of at least a curing
agent and a curable insulating resin while maintaining the
stretched state. As the stretchable film, although a known resin
film or the like can be used, the use of a homopolymer or copolymer
of polyethylene resin, polypropylene resin, polyester resin,
polyvinyl alcohol resin, polyvinylbutyral resin, polyvinylidene
chloride resin or the like, or a flexible and stretchable film of a
resin such as nitryl rubber, butadiene rubber, silicone rubber is
preferable. Polypropylene resin and polyester resin are
particularly preferable. The shrinking percentage after stretching
is preferably 10% or less, and more preferably 5% or less.
As a method for dispersing, arranging and fixing conductive
particles on a stretchable film, a known method can be used. For
example, a method wherein an adhesive layer containing at least a
thermoplastic resin is formed on the stretchable film, conductive
particles are contacted and deposited thereon, and they are
arranged in a single layer by applying load using a rubber roll can
be adopted. In this case, to pack the conductive particles without
gaps, repetition of deposition and rolling steps for several times
is preferable. Since closest packing is the most stable structure
in the case of spherical conductive particles, the conductive
particles can be relatively easily packed. Alternatively, a method
wherein an adhesive is applied onto the stretchable film to form an
adhesive layer, conductive particles are adhered thereon, and
adhesion is repeated several times, if required, to disperse and
arrange the conductive particles in a singly layer: a method
wherein a stretchable film is charged, the conductive particles are
dispersed and adhered in a single layer and the like can be
used.
Although a known methods can be used as a method for stretching a
stretchable film on which a single layer of conductive particles is
arranged, from the aspect of even diffusing and arranging, the use
of biaxial stretching equipment is preferable. From the aspect of
distance between particles, the percentage of stretching is
preferably 80% or more and 400% or less, more preferably 100% or
more and 300% or less. Stretching by 100% means that the length of
the portion stretched along the stretching direction is 100% the
length of the film before stretching. Although the stretching
direction is optional, biaxial stretching of a stretching angle of
90.degree. is preferable, and simultaneous stretching is
preferable. Although the stretching direction is optional, biaxial
stretching of a stretching angle of 90.degree. is preferable, and
simultaneous stretching is preferable. In the case of biaxial
stretching, the percentage of stretching in each direction can be
either same or different. As the biaxial stretching equipment,
simultaneous biaxial continuous stretching equipment is
preferable.
Although a known equipment can be used as the simultaneous biaxial
continuous stretching equipment, a tenter-type stretching machine
wherein long sides are fixed by chuck fittings, and the distances
between them are simultaneously stretched in length and width
directions to conduct continuous stretching is preferable. As the
system to adjust stretching percentage, although a screw system or
a pantograph system can be used, in view of the adjustment
accuracy, the pantograph system is more preferable. In the case of
stretching while heating, it is preferable to install a preheating
zone before the stretching portion, and to install a heat fixing
zone after the stretching portion.
As the method for manufacturing an anisotropic conductive adhesive
sheet from the state wherein the conductive particles are dispersed
and arranged by arranging a single layer of conductive particles on
a stretchable film and stretching them, the use of a method wherein
a previously fabricated adhesive sheet composed of at least a
curable insulating resin is stacked, and conductive particles or an
adhesive film containing conductive particles is transferred, is
preferable. A method wherein a solution containing at least an
insulating resin is applied in the dispersed and arranged state,
and dried, then the anisotropic conductive adhesive sheet is peeled
off the stretchable sheet or the like, can be used.
The anisotropic conductive adhesive sheet of the present invention
can be a single-layer sheet or a laminate sheet wherein an adhesive
sheet not containing conductive particles but containing at least
an insulating resin is stacked. The film thickness of the adhesive
sheet to be stacked is preferably thinner than the film thickness
of the adhesive sheet containing conductive particles.
As the curable insulating resin used in the present invention, a
thermosetting resin, a photo-curable resin, a thermosetting and
photocurable resin, and an electron beam-curable resin can be used.
For the ease of handling, the use of a thermosetting insulating
resin is preferable. Although epoxy resin, acrylic resin and the
like can be used as the thermosetting resin, epoxy resin is
particularly preferable. The epoxy resin is a compound having 2 or
more epoxy groups in the molecule, and a compound having a
glycidylether group, a glycidylester group, or an alicyclic epoxy
group, and a compound wherein a double bond in the molecule is
epoxidized are preferable. Specifically, bisphenol-A-type epoxy
resin, bisphenol-F-type epoxy resin, naphthalene-type epoxy resin,
novolak-phenol-type epoxy resin, or modified epoxy resin thereof
can be used.
The curing agent used in the present invention can by any curing
agent that can cure the above-described thermosetting insulating
resins. When a thermosetting resin is used as the curable
insulating resin, the agent that reacts with the thermosetting
resin at 100.degree. C. or above to cure it is preferable. In the
case of epoxy resin, from the aspect of storage properties, a
latent curing agent is preferable, and for example, an imidazole
curing agent, a capsule-type imidazole curing agent, a cationic
curing agent, a radical curing agent, a Lewis acid curing agent, an
amine imide curing agent, a polyamine salt curing agent, a
hydrazide curing agent, or the like can be used. From the aspects
of storage properties and low-temperature reactivity, the
capsule-type imidazole curing agent is preferable.
To the anisotropic conductive adhesive sheet of the present
invention, besides the curing agent and curable insulating resin, a
thermoplastic resin or the like can be compounded. By compounding a
thermoplastic resin, a sheet can be easily formed. The compounding
quantity in this time is preferably 200% by mass, more preferably
100% by mass of the combined components of the curing agent and
curable insulating resin. The thermoplastic resin that can be
compounded in the present invention is phenoxy resin, polyvinyl
acetal resin, polyvinyl butyral resin, alkylated cellulose resin,
polyester resin, acrylic resin, styrene resin, urethane resin,
polyethylene terephthalate resin, and the like. Such resins can be
selectively used alone or in a combination of two or more. Among
these resins, a resin having a polar group, such as hydroxyl and
carboxyl groups, is preferable from the aspect of adhesive
strength. Furthermore, it is preferable that the thermoplastic
resin contains one or more thermoplastic resin having a glass
transition temperature of 80.degree. C. or above.
In the anisotropic conductive adhesive sheet of the present
invention, additives can be compounded to the above-described
components. In order to improve the adhesion between the
anisotropic conductive adhesive sheet and the deposited material, a
connecting agent can be compounded as an additive. As the
connecting agent, although a silane connecting agent, titanium
connecting agent, or aluminum connecting agent can be used, the
silane connecting agent is preferable. As the silane connecting
agent, .gamma.-glycidoxypropyltrimethoxysilane,
.gamma.-glycidoxypropyltriethoxysilane,
.gamma.-mercaptotrimethoxysilane,
.gamma.-aminopropyltrimethoxysilane,
.beta.-aminoethyl-.gamma.-aminopropyltrimethoxysilane,
.gamma.-ureidopropyltrimethoxysilane, or the like can be used. The
compounding quantity of the connecting agent is preferably 0.01
part by mass to 1 part by mass based on 100 parts by mass of the
combination of the curing agent and curable insulating resin. In
view of improving adhesion, 0.01 part by mass or more is preferable
and in view of reliability, 1 part by mass or less is
preferable.
Furthermore, in order to prevent the lowering of insulating
properties due to ionic components in the anisotropic conductive
adhesive sheet when absorbing moisture, an ion scavenger can be
compounded as an additive. As the ion scavenger, although an
organic ion exchanger, an inorganic ion exchanger, an inorganic ion
adsorbing agent, or the like can be used, an inorganic ion
exchanger, which has excellent heat resistance, is preferable. As
the inorganic ion exchanger, a zirconium compound, a
zirconium-bismuth compound, an antimony-bismuth compound, a
magnesium-aluminum compound, or the like can be used. Although the
types of ions to be exchanged include a cation type, an anion type,
and an amphoteric ion type, the amphoteric ion type is preferable
because it can exchange both metal ions (cations), which directly
cause ion migration, and anions, which cause the elevation of
electrical conductivity and the formation of metal ions. The
average particle size of the ion scavenger to be compounded is
preferably 0.01 .mu.m or more and 5 .mu.m or less, more preferably
0.01 .mu.m or more and 1 .mu.m or less.
Next, a method for manufacturing the anisotropic conductive
adhesive sheet of the present invention will be described.
First, an adhesive layer is provided on a biaxially stretchable
film to form a laminate, conductive particles having an average
particle size of 1 to 8 .mu.m are closely packed on the laminate to
fabricate a conductive-particle adhered film, the
conductive-particle adhered film is biaxially stretched and held so
that the average particle distance between the conductive particles
and adjacent particles is at least once but five times or less the
average particle size of the conductive particles and 20 .mu.m or
less, and the conductive particles are transferred on an adhesive
sheet containing at least a curing agent and a curable insulating
resin and having a thickness of 1.5 times or more the average
particle distance of the conductive particles and 40 .mu.m or less,
to manufacture the anisotropic conductive adhesive sheet of the
present invention. Preferably, the biaxially stretchable film is a
long film, and the adhesive sheet is also a long adhesive
sheet.
Although known adhesives can be used in the adhesive layer, when
biaxial stretching is performed while heating, the use of a
non-thermal cross-linking adhesive is preferable. Specifically, a
natural rubber latex adhesive, a synthetic rubber latex adhesive, a
synthetic resin emulsion adhesive, silicone adhesive,
ethylene-vinyl acetate copolymer adhesive, and the like can be used
alone or in combination. As the adhesion of the adhesive, the
peeling strength of the surface of the surface metal of the
conductive particles to be used is preferably within a range
between 0.5 gf/cm and 40 gf/cm, more preferably within a range
between 1 gf/cm and 20 gf/cm. As the measuring method, a method
wherein a glass plate coated with a metal having the same
composition as the surface metal of the conductive particles is
prepared, a film having a width of 2 cm coated with the adhesive is
adhered, and 90.degree. peeling strength is measured, can be used.
In view of holding the conductive particles when the conductive
particles are adhered and when the film is stretched, the peeling
strength is preferably 0.5 gf/cm or more; and in view of
transferring particles to the adhesive sheet after stretching, the
peeling strength is preferably 40 gf/cm or less. The thickness of
the adhesive layer is preferably within a range between 1/50 and
twice, more preferably 1/10 and once the average particle size of
the conductive particles to be used. In view of holding the
conductive particles when the conductive particles are adhered and
when the film is stretched, the thickness is preferably 1/50 or
more the average particle size of the conductive particles; and in
view of transferring particles to the adhesive sheet after
stretching, the thickness is preferably twice or less. As the
method for forming the adhesive layer, a method wherein the
adhesive dispersed or dissolved in a solvent or water is applied
using a heretofore known method, such as a gravure coater, die
coater, knife coater, bar coater, or the like, and dried, can be
used. When a hot-melt-type adhesive is applied, roll coating
without solvent can be performed.
As the method for closely packing the conductive particles, the
above-described method wherein conductive particles are dispersed
and arranged on a stretchable film and fixed can be used.
The film thickness of the film after stretching is preferably 1/10
to once, more preferably 1/5 to 1/2 of the sum of the film
thickness of the adhesive sheet to be transferred and the support
film of the adhesive sheet. In view of handling the film after
stretching, the film thickness is preferably 1/10 or more of the
sum of the film thickness; and in view of transferring particles to
the adhesive sheet after stretching, the film thickness is
preferably once or less of the sum of the film thickness.
The present invention also relates to a method for electrically
connecting an electronic circuit component having fine connecting
terminals to a circuit board having a circuit corresponding to the
electronic circuit component using an anisotropic conductive
adhesive sheet. In the fine connecting method, the height of the
fine connecting terminal of the electronic circuit component is 3
to 15 times the average particle distance of the conductive
particles but not greater than 40 .mu.m, the distance between the
fine connecting terminals is 1 to 10 times the average particle
distance but not greater than 40 .mu.m, and the pitch of the fine
connecting terminals is 3 to 30 times the average particle distance
of the conductive particles but not greater than 80 .mu.m. The
electronic circuit component is electrically coupled to the circuit
board having a circuit corresponding to the electronic circuit
component using the anisotropic conductive adhesive sheet of the
present invention.
The height of the connecting terminal is 3 to 15 times the average
particle distance of the conductive particles but not greater than
40 .mu.m, and 4 to 10 times are preferable. In view of the
mechanical strength of the connecting structure, not less than 3
times are preferable; and in view of the movement of conductive
particles due to the resin flow of the adhesive sheet occurring in
connecting, the lowering of connecting properties due to lowered
number of conductive particles in the lower portion of the
connecting terminal, the movement of conductive particles present
in the area other than the connecting portion, and the lowering of
insulating properties due to coagulation, not more than 15 times
and not more than 40 .mu.m are preferable. The distance between
connecting terminals is once to 10 times the average particle
distance but not greater than 40 .mu.m, preferably once to 10 times
but not greater than 20 .mu.m, and more preferably 2 to 5 times but
not greater than 15 .mu.m. In view of insulating properties, once
or more is preferable and in view of fine connecting, not more than
10 times and not greater than 40 .mu.m is preferable. The pitch is
3 to 30 times the average particle distance but not greater than 80
.mu.m, and preferably 5 to 20 times but not greater than 40 .mu.m.
In view of connecting properties, 3 times or more is preferable;
and in view of fine connecting, not more than 30 times but not
greater than 80 .mu.m is preferable.
The present invention also relates to a fine connecting structure
connected by the above-described fine connecting method.
The material of the circuit bard coupled using an anisotropic
conductive adhesive sheet of the present invention can be either an
organic board or an inorganic board. As the organic board, a
polyimide film board, a polyamide film board, a polyethersulfone
film board, a rigid board produced by impregnating epoxy resin into
glass cloth, a rigid board produced by impregnating
bismaleimide-triazine resin into glass cloth, or the like can be
used. As the inorganic board, a silicon board, a glass board, an
alumina board, an aluminum nitride board, or the like can be used.
As the wiring material for a wiring board, an inorganic wiring
material, such as indium tin oxide, indium zinc oxide or the like;
a metal wiring material, such as gold-plated copper,
chromium-copper, aluminum and gold bumps; a composite wiring
material wherein an inorganic wiring material such as indium tin
oxide is covered with a metallic material, such as aluminum and
chromium, or the like can be used.
The distance between connecting circuits used in the present
invention is preferably 3 to 500 times the average particle size of
conductive particles in view of electrical insulating properties.
In the connecting circuit used in the present invention, the
connecting area of the circuit portion to be connected is
preferably 1 to 10000 times the square of the value of the
above-described average particle size. From the aspect of
connecting properties, 2 to 100 times are particularly
preferable.
The anisotropic conductive adhesive sheet of the present invention
or the connecting structure of the present invention can be used
for connecting the display device, such as a liquid crystal display
device, a plasma display device, and an electroluminescence display
device to a wiring board; mounting electronic parts, such as an
LSI, of these devices; connecting other devices to a wiring board;
and mounting electronic parts, such as an LSI. Among the
above-described display devices, the anisotropic conductive
adhesive sheet or the connecting structure can be suitably used in
the plasma display device, and the electroluminescence display
device, which require reliability.
Next, the present invention will be described in further detail
referring to examples and comparative examples.
EXAMPLE 1
In an ethyl acetate-toluene mixed solvent (mixing ratio of 1:1), 37
g of a phenoxy resin (glass transition temperature: 98.degree. C.,
number average molecular weight: 14000), 26 g of a bisphenol-A-type
epoxy resin (epoxy equivalent: 190, viscosity at 25.degree. C.:
14000 mPaS), and 0.3 g of .gamma.-glycidoxypropyltrimethoxysilane
were dissolved to produce a solution having a solid content of
50%.
In the solution having a solid content of 50%, 37 g of a liquid
epoxy resin containing a microcapsule-type latent imidazole curing
agent (average particle size of the microcapsules: 5 .mu.m,
activating temperature: 125.degree. C.) was compounded and
dispersed. Thereafter, the dispersion was applied onto a
polyethylene terephthalate film having a thickness of 50 .mu.m,
wind-dried at 60.degree. C. for 15 minutes to obtain a film-like
adhesive sheet having a film thickness of 20 .mu.m.
Onto a non-stretched polypropylene film having a thickness of 45
.mu.m coated with a nitrile rubber latex-methyl methacrylate graft
copolymer adhesive having a thickness of 5 .mu.m, a single layer of
gold-plated plastic particles of an average particle size of 3.0
.mu.m were applied so as to be substantially free of gaps.
Specifically, a container having a width larger than the width of
the film packed with the gold-plated plastic particles so as to
have a thickness of several layers was prepared, the film with the
adhesive applied surface facing downward was pressed against the
gold-plated particles to adhere, and thereafter, excessive
particles were scraped down with a scraper made of a non-woven
fabric. By repeating this procedure twice, a single-layer coated
film without gaps was obtained. The particle size distribution of
the gold-plated plastic particles was previously measured using a
laser particle size distribution meter (HELOS SYSTEM, manufactured
by JEOL), and the value at 50% cumulative value was made to be the
average particle size. The film was fixed using a biaxial
stretching equipment (corner stretching type biaxial stretching
equipment of pantograph system, X6H-S manufactured by Toyo Seiki
Seisaku-sho, Ltd.) using 10 chucks in each of lengthwise and
crosswise directions, preheated at 150.degree. C. for 120 seconds,
then, stretched by 100% in each of lengthwise and crosswise
directions at a rate of 20%/sec and fixed. After stacking the
adhesive sheet on the stretched film, the adhesive sheet was peeled
off to obtain an anisotropic conductive adhesive sheet. From the
conductive particles on the obtained anisotropic conductive
adhesive sheet, 100 particles were randomly selected, and the
distance from the surface of the anisotropic conductive adhesive
sheet was measured using a laser microscope that can measure the
displacement in the focal point direction (VK9500, manufactured by
Keyence Corporation, shape measurement resolution: 0.01 .mu.m). As
a result, it was known that 95% of the conductive particles were
present within the layer shown in a range of 5.5 .mu.m in the film
thickness direction of the anisotropic conductive adhesive sheet.
Of the 100 measured conductive particles, 92% were single
particles. The average distance between particles was 4.17 .mu.m,
which was 1.39 times the average particle size.
EXAMPLE 2
In an ethyl acetate-toluene mixed solvent (mixing ratio: 1:1), 42 g
of a phenoxy resin (glass transition temperature: 45.degree. C.,
number average molecular weight: 12000), 32 g of a naphthalene-type
epoxy resin (epoxy equivalent: 136, semisolid), and 0.06 g of
.gamma.-ureidopropyltrimethoxysilane were dissolved to produce a
solution having a solid content of 50%. In the solution having a
solid content of 50%, 26 g of a liquid epoxy resin containing a
microcapsule-type latent imidazole curing agent (average particle
size of the microcapsules: 5 .mu.m, activating temperature:
125.degree. C.) was compounded and dispersed. Thereafter, the
dispersion was applied onto a polyethylene terephthalate film
having a thickness of 50 .mu.m, wind-dried at 60.degree. C. for 15
minutes to obtain a film-like adhesive sheet having a film
thickness of 15 .mu.m.
Onto a non-stretched polypropylene film having a thickness of 45
.mu.m coated with a nitrile rubber latex-methyl methacrylate graft
copolymer adhesive having a thickness of 5 .mu.m, a single layer of
gold-plated plastic particles of an average particle size of 2.5
.mu.m were applied in the same manner as in Example 1 so as to be
substantially free of gaps. The film was stretched using biaxial
stretching equipment by 120% in each of lengthwise and crosswise
directions in the same manner as in Example 1, and fixed. After
stacking the adhesive sheet on the stretched film, the adhesive
sheet was peeled off to obtain an anisotropic conductive adhesive
sheet. From the conductive particles on the obtained anisotropic
conductive adhesive sheet, 100 particles were randomly selected,
and the distance from the surface of the anisotropic conductive
adhesive sheet was measured using a laser displacement gage. As a
result, it was known that 95% of the conductive particles were
present within the layer shown in a range of 4.8 .mu.m in the film
thickness direction of the anisotropic conductive adhesive sheet.
Of the 100 measured conductive particles, 91% were single
particles. The average distance between particles was 4.24 .mu.m,
which was 1.70 times the average particle size.
EXAMPLE 3
In an ethyl acetate-toluene mixed solvent (mixing ratio: 1:1), 15 g
of a phenoxy resin (glass transition temperature: 45.degree. C.,
number average molecular weight: 12000), 24 g of a phenoxy resin
(glass transition temperature: 98.degree. C., number average
molecular weight: 14000), 26 g of a naphthalene-type epoxy resin
(epoxy equivalent of 136, semisolid), and 0.1 g of
.gamma.-glycidoxypropyltrimethoxysilane were dissolved to produce a
solution having a solid content of 50%. In the solution having a
solid content of 50%, 35 g of a liquid epoxy resin containing a
microcapsule-type latent imidazole curing agent (average particle
size of the microcapsules: 5 .mu.m, activating temperature:
125.degree. C.) was compounded and dispersed. Thereafter, the
dispersion was applied onto a polyethylene terephthalate film
having a thickness of 50 .mu.m, wind-dried at 60.degree. C. for 15
minutes to obtain a film-like adhesive sheet A having a film
thickness of 15 .mu.m.
Furthermore, a film-like adhesive sheet B having a film thickness
of 5 .mu.m was obtained in the same manner as described except that
a polyethylene terephthalate film undergone easy-peeling treatment
was used.
Onto a non-stretched polypropylene film having a thickness of 45
.mu.m coated with a nitrile rubber latex-methyl methacrylate graft
copolymer adhesive having a thickness of 5 .mu.m, a single layer of
gold-plated nickel particles of an average particle size of 2.6
.mu.m were applied in the same manner as in Example 1 so as to be
substantially free of gaps. The film was stretched using biaxial
stretching equipment by 200% in each of lengthwise and crosswise
directions in the same manner as in Example 1, and fixed. After
stacking the adhesive sheet A on the stretched film, the adhesive
sheet was peeled off, and the adhesive sheet B was stacked on the
peeled surface to obtain an anisotropic conductive adhesive sheet.
From the conductive particles on the obtained anisotropic
conductive adhesive sheet, 100 particles were randomly selected,
and the distance from the surface of the anisotropic conductive
adhesive sheet was measured using a laser displacement gage. As a
result, it was known that 95% of the conductive particles were
present within the layer shown in a range of 4.9 .mu.m in the film
thickness direction of the anisotropic conductive adhesive sheet.
Of the 100 measured conductive particles, 91% were single
particles. The average distance between particles was 7.22 .mu.m,
which was 2.77 times the average particle size.
COMPARATIVE EXAMPLE 1
In an ethyl acetate-toluene mixed solvent (mixing ratio of 1:1), 37
g of a phenoxy resin (glass transition temperature: 98.degree. C.,
number average molecular weight: 14000), 26 g of a bisphenol-A-type
epoxy resin (epoxy equivalent: 190, viscosity at 25.degree. C.:
14000 mPaS), and 0.3 g of .gamma.-glycidoxypropyltrimethoxysilane
were dissolved to produce a solution having a solid content of
50%.
In the solution having a solid content of 50%, 37 g of a liquid
epoxy resin containing a microcapsule-type latent imidazole curing
agent (average particle size of the microcapsules: 5 .mu.m,
activating temperature: 125.degree. C.), and 2.0 g of gold-plated
plastic particles having an average particle size of 3.0 .mu.m was
compounded and dispersed. Thereafter, the dispersion was applied
onto a polyethylene terephthalate film having a thickness of 50
.mu.m, wind-dried at 60.degree. C. for 15 minutes to obtain a
film-like anisotropic adhesive sheet having a film thickness of 20
.mu.m.
From the conductive particles on the obtained anisotropic
conductive adhesive sheet, 100 particles were randomly selected,
and the distance from the surface of the anisotropic conductive
adhesive sheet was measured using a laser displacement gage. As a
result, it was known that conductive particles were randomly
present in the film thickness direction of the anisotropic
conductive adhesive sheet. Of the 100 measured conductive
particles, 75% were single particles.
COMPARATIVE EXAMPLE 2
In an ethyl acetate-toluene mixed solvent (mixing ratio of 1:1), 42
g of a phenoxy resin (glass transition temperature: 45.degree. C.,
number average molecular weight: 12000), 32 g of a naphthalene-type
epoxy resin (epoxy equivalent of 136, semi-solid), and 0.06 g of
.gamma.-ureidopropyltrimethoxysilane were dissolved to produce a
solution having a solid content of 50%. In the solution having a
solid content of 50%, 26 g of a liquid epoxy resin containing a
microcapsule-type latent imidazole curing agent (average particle
size of the microcapsules: 5 .mu.m, activating temperature:
125.degree. C.), and 6.0 g of gold-plated nickel particles having
an average particle size of 2.6 .mu.m was compounded and dispersed.
Thereafter, the dispersion was applied onto a polyethylene
terephthalate film having a thickness of 50 .mu.m, wind-dried at
60.degree. C. for 15 minutes to obtain a film-like anisotropic
adhesive sheet having a film thickness of 20 .mu.m.
From the conductive particles on the obtained anisotropic
conductive adhesive sheet, 100 particles were randomly selected,
and the distance from the surface of the anisotropic conductive
adhesive sheet was measured using a laser displacement gage. As a
result, it was known that conductive particles were randomly
present in the film thickness direction of the anisotropic
conductive adhesive sheet. Of the 100 measured conductive
particles, 70% were single particles.
COMPARATIVE EXAMPLE 3
As anisotropic conductive adhesive sheet was obtained in the same
manner as in Example 1 except that gold-plated plastic particles of
an average particle size of 10 .mu.m were used, and the sheet was
stretched by 60%. From the conductive particles on the obtained
anisotropic conductive adhesive sheet, 100 particles were randomly
selected, and the distance from the surface of the anisotropic
conductive adhesive sheet was measured using a laser displacement
gage. As a result, it was known that 96% of the conductive
particles were present within the layer shown in a range of 19.2
.mu.m in the film thickness direction of the anisotropic conductive
adhesive sheet.
Of the 100 measured conductive particles, 93% were single
particles. The average distance between particles was 8.52 .mu.m,
which was 0.85 times the average particle size.
(Method for Measuring Connecting Resistance Value)
After forming an oxide film on the entire surface of a silicon
piece (thickness: 0.5 mm) having a width of 1.6 mm and a length of
15.1 mm, 175 and 16 thin aluminum films (1000 angstroms) each
having a width of 74.5 .mu.m and a length of 120 .mu.m were formed
on the long side and the short side, respectively, 40 .mu.m inside
of the peripheral portions, so that the each distance between films
becomes 0.1 .mu.m. In order to form two gold bumps (thickness: 15
.mu.m) each having a width of 25 .mu.m and a length of 100 .mu.m on
each of these thin aluminum films so as to have a distance of 15
.mu.m, on the portion other than an opening having a width of 10
.mu.m and a length of 85 .mu.m on 7.5 .mu.m inside of the
peripheral portion of the gold-bump disposing position, a polyimide
protective film was formed on the entire surface other than the
above-described opening using a normal method. Thereafter, the
above-described gold bumps were formed to be test chips.
On alkali-free glass of a thickness of 0.7 mm, a connecting pad
(width: 66 .mu.m, length: 120 .mu.m) of indium-tin oxide
(thickness: 1400 angstrom) was formed so as to be connected in the
position relationship to be a pair with a gold bump on the thin
aluminum film adjacent to a gold bump on the above-described thin
aluminum film. Each time 20 gold bumps were connected, an outgoing
wiring of a thin indium-tin oxide was formed on the above-described
connecting pad, and a thin aluminum-titanium film (titanium: 1%,
3000 angstroms) was formed on the outgoing wiring to be a
connecting evaluating board. On the above-described connecting
evaluating board, an anisotropic conductive adhesive sheet having a
width of 2 mm and a length of 17 mm was temporarily bonded so that
the entire connecting pad was covered, and after pressing at
80.degree. C. under 0.3 MPa for 3 seconds using a pressure bonding
head of a width of 2.5 mm, the base film of polyethylene
terephthalate was peeled off. A test chip was placed thereon so
that the locations of the above-described connecting pad and gold
bump are aligned and pressure-bonded at 220.degree. C. for 5
seconds under 5.2 MPa. After pressure bonding, the resistance value
between the above-described outgoing wirings (daisy chain of 20
gold bumps) was measured using a resistance meter of a 4-terminal
method to be a connecting resistance value.
(Method for Testing Insulation Resistance)
On alkali-free glass of a thickness of 0.7 mm, a connecting pad
(width: 65 .mu.m, length: 120 .mu.m) of indium-tin oxide (1400
angstrom) was formed in the position relationship so that 2 gold
bumps on the above-described thin aluminum film could be coupled to
each other. A connecting wiring of a thin indium-tin oxide was
formed so that 5 connecting pads could be alternately coupled, and
another connecting wiring of a thin indium-tin oxide was formed so
that 5 connecting pads could be alternately coupled so as to be
pair with them and form a comb-shaped pattern. On each connecting
wiring, an outgoing wiring of a thin indium-tin oxide film was
formed, and a thin aluminum-titanium film (titanium: 1%, 3000
angstroms) was formed on the outgoing wiring to be an insulating
property evaluating board. On the above-described insulating
property evaluating board, an anisotropic conductive adhesive sheet
having a width of 2 mm and a length of 17 mm was temporarily bonded
so that the entire connecting pad was covered, and after pressing
at 80.degree. C. under 0.3 MPa for 3 seconds using a pressure
bonding head of a width of 2.5 mm, the base film of polyethylene
terephthalate was peeled off. A test chip was placed thereon so
that the locations of the above-described connecting pad and gold
bump are aligned and pressure-bonded at 220.degree. C. for 5
seconds under 2.6 MPa to be an insulating resistance testing
board.
While holding the insulating resistance testing board at 60.degree.
C. and a relative humidity of 90%, a DC voltage of 100 V was
impressed between paired outgoing wirings using a constant-voltage
constant-current power source. The insulation resistance between
these wirings was measured once every 5 minutes, and time until the
insulation resistance value becomes 10 M.OMEGA. or less was
measured to be an insulation lowering time. The case when the
insulation lowering time was less than 240 hours was evaluated as
.times. (bad), and the case of 240 hours or more was evaluated as
.largecircle. (good);
The above results are shown in Table 1.
TABLE-US-00001 TABLE 1 Connection resistance Insulation value
resistance (.OMEGA.) test Example 1 12.4 .largecircle. (good)
Example 2 11.9 .largecircle. (good) Example 3 13.5 .largecircle.
(good) Comparative 26.2 X (bad) Example 1 (short-circuiting)
Comparative 14.0 X (bad) Example 2 (short-circuiting, initial)
Comparative 13.1 X (bad) Example 3 (short-circuiting, initial)
As is obvious from Table 1, the anisotropic conductive adhesive
according to the present invention exerts very excellent insulation
reliability.
INDUSTRIAL APPLICABILITY
The anisotropic conductive adhesive sheet according to the present
invention exerts low connecting resistance and high insulation
reliability, and is suitable as a bare chip connecting material
wherein fine circuit connecting is required, and a connecting
material for a high-definition display device and the like.
* * * * *